Frank Stocklin

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SUPERNOVA/ACCELERATION PROBE (SNAP)
Data Systems

• Frank Stocklin
• Ron Vento
• Leslie Ambrose
• June 28,2001

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Data SystemsTopics

• Overview
• Driving Requirements and Assumptions
• Selected Configuration and Rationale
• Coverage
• Signal Margin Summary
• Component Power/Mass/Cost Summary
• Risk Assessment
• Issues and Concerns
• Backup

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Data SystemsOverview

• Ka-Band downlink _at_ 55 Mbps continuously (except
  during eclipse) through a HGA to a ground network
  consisting of either
• Berkeley, CA Lyon, France Tokyo, Japan
• Single gaps of 18 hours will occur each orbital
  period of 14 days
• 18 hour gaps are acceptable at once per orbit
• S-Band TC through omni antennas
• S-Band ranging using DSN during early maneuvers,
  infrequently during the mission
• Ground terminal sized for maximum range of 69 Re
• On-board recorder sized for recording
  spectrograph data and housekeeping for 24 hours

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Data SystemsDriving Requirements Assumptions

• Launch Dec 2008
• Mission Life 2 year required, 5 year goal
• Nominal Orbit Prometheus 57Re x 19Re _at_ 40 deg
• Stellar pointing
• Instrument Data Collection Rates
• 45.2 Mbps
• Housekeeping rate 16 Kbps
• CCSDS compatible (_at_ 15)
• Data storage 24 hrs/72 Gbits (see CDH for
  details)

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Data SystemsDriving Requirements Assumptions

• Data Latency None
• Infrequent commanding
• Telemetry BER 10-6
• Rate 1/2 Convolutional/Reed-Solomon encoding
• Inclination is primary driver
• CCSDS compatible
• Redundancy
• Link margins 3 dB
• S/C is jitter sensitive

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Data SystemsSelected Configuration Rationale

• Ka-Band
• 3 gimbaled 0.7m antennas
• antenna movements between observation periods
  (every 100-400 seconds)
• Beamwidth of 1 deg is large enough to provide
  adequate coverage without movement during
  observation periods (will stay close enough to
  main beam so as not to degrade the link)
• located 120 deg apart
• switchable by on-board command
• 20 watt TWT(2)- heritage is TDRS H
• Ka-Band modulators(2)-modification to existing L3
  X Band transmitter
• Data rate 55 Mbps continuous (includes science,
  Hskpg, CCSDS R/S encoding)
• S-Band
• Omni antennas
• Transponders(2)
• Command rate 2 Kbps
• Telemetry rate 1 Kbps

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Data SystemsSelected Configuration Rationale

• Normal operations
• Continuous Ka-band transmission
• Both S-band receivers always on
• S-band transmitter on as needed
• Ground terminals
• Ground terminals are sized for maximum range of
  69 Re
• Ka-band autotrack will be required
• Berkeley 11m (modified for Ka-Band)
• All other sites 10m
• Ka-band receive
• S Band receive/transmit
• Radomes highly recommended included in cost

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Data SystemsSelected Configuration Rationale

• Operational scenario 1(Berkeley,France,Japan)
• Inclinations
• Continuous transmission
• Worst case maximum gap 18 hours (average outage
  12 hours)
• per orbital period of 14 days(nominal period)
• Operational workaround understood to be
  acceptable with spectrograph data(approx 816
  Kbps) recorded on board played back during
  visible periods

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Data SystemsS/C Antenna Considerations

• S-Band
• Need 2 antennas to enable reliable command
  recovery in case of loss of control launch
  phase support
• Best location is perpendicular to pointing
  axis(Z)
• Ka- Band
• Need 3 antennas in order to keep the antennas
  close to the spacecraft so that the dampening of
  the movement is quicker
• Best location is perpendicular to the pointing
  axis

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Data SystemsSelected Configuration Rationale
SNAP
55 Mbps K-Band science 1 kbps S-Band hskpg
55 Mbps K-Band science 1 kbps S-Band hskpg
2 kbps S-Band Cmd
2 kbps S-Band Cmd
10M K/S
11M K/S
SNAP MOC
Japan/France
Berkeley
Command
Science Hskpg
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Data SystemsSelected Configuration and Rationale
Diplexer
OMNI 1
S-Band XPNDR
Hybrid
CMD/TLM
S-Band XPNDR
Diplexer
OMNI 2
CDH
Instruments
HGA
Switch
K-Band Modulator(2)
K-Band Amplifier(2)
Science
HGA
Data Storage 9 Gbytes
HGA
OBC
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SNAPCoverage Gaps (3 stations)

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SNAP Signal Margins (Max Range 69 Re)

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Data Systems Component
Power/Mass/Cost Summary
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Data SystemsRisk Assessment

• Construction, Maintenance and operation of 10M
  Ka/S-band stations Low to Medium Risk
• K-band Modulator Modified design of current
  X-band transmitter Low to Medium Risk

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Data SystemsIssues and Concerns

• During 5 year period the apogee/perigee/inclinatio
  n will vary
• Apogee up to 69 Re
• Perigee down to 7 Re
• Inclination down to 0 deg up to 65 deg Shape of
  the orbit
• If the inclination increases coverage gap times
  will increase (gaps greater than 18 hours will
  occur when the inclination increases above 40
  deg.)
• Location of apogee and perigee (dependent on
  possible inclinations)

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Data SystemsSNAP

• Back-Up Charts

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SNAP Ka-Band 10 M Downlink (55 Mbps)
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SNAP S-Band 10M Uplink (2 kbps)
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SNAP S-Band Downlink (2 Kbps)
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SNAP S-Band Downlink (1 kbps)
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SNAP S-band Ranging Up-link
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SNAP S-band Ranging Downlink